Young Dai lives on Dermline Island, where he dreams of being a Hero. One day, a Hero and his companions come to the island. Dai is excited at first, but their true intent is to steal his best friend, Gomechan, the mythical Golden Metal Slime.

Dai must take Leona to the Earth Cave for a ritual; Dai dislikes Leona at first, though they slowly come to understand each other; when a giant scorpion attacks, Dai defeats it, but Leona is poisoned.

A dark power affects Dai's monster friends, driving them berserk. Brass tries to get Dai to leave and as they argue, a Hero trainer arrives to inform Dai that the Dark Lord has returned.

Avan turns into a dragon and attacks Dai, who fights back to no avail; as Dai clears his objective, someone enters the island.

To protect his students and the world, Avan gathers the last of his strength and faces Hadlar, while Dai can do nothing but watch.

Dai decides to carry on Avan's will and leaves the island; Popp joins Dai and they head to Romos Castle.